This is one of those games that you can't really say much about without delving into significant spoilers given that it is heavily narrative-driven. That makes it hard to review in detail, but I think there are definitely things that can be said about it in isolation. I'll spoiler tag anything I think could theoretically spoil a no-prior-knowledge run but remain vague beyond describing the first 10 mins or so of the game.
The first thing I'd preface to anyone considering playing this game is that it's extremely dark. Even games like Silent Hill I feel you can weirdly find some kind of positive interpretation or lesson learned that provides an upside. That sort of thing is nearly absent here. While some may disagree, I don't feel at all like this game is just trying to be edgy. The content is purposeful and follows a logical string of events exploring important issues. But it does not pull its punches at any point, nor does it shy away from agonizing conclusions. It is exploring a dark time and dark events and is uninterested in lightening their narrative load. There is some visualization of extremely uncomfortable situations including (spoiler tagged in case you don't care about the content warning and want to go in without the prior knowledge, but I stayed vague) violence against self, physical and verbal abuse, and inappropriate relationships. I wouldn't recommend the game to anyone with sensitivity toward those subjects.
However, there is certainly an underlying tragic beauty to Detention that makes it rise beyond mere misery porn. Unfortunately this most important paragraph is where I feel I must be extra vague as this is a game that is best experienced first-hand. The game explores its themes with a great deal of depth and one of my favorite things about it is that it feeds its clues to you very gradually and with some degree of subtlety, but in a way that I still found it quite easy to follow. Convoluted but interesting narratives can be fun, but I have expressed some frustration with games I feel you need to replay several times or watch YouTube commentaries to even understand the basic plot of. I didn't really feel that way with this game despite its often symbolic narrative and non-linear revelations seen through the eyes of an unreliable narrator. I did go ahead and look up more about the game online and other than missing the true ending (some say "good" ending but lol), I didn't really misunderstand or miss anything significant in the game. I will say vaguely that while tragic themes litter almost the whole story, there is definitely a message beyond simply "damn, shit sucks," even if that message is one of the least subtle aspects of the game.
One of my favorite things about Detention is that I came to it looking for a particularly Taiwanese horror experience (the studio is Taiwanese in case that was unclear). I've been interested in playing horror games from different parts of the world as not only is it a genre I enjoy, but I think you can learn a lot about a culture from its horror. Accordingly, while there is no requirement or expectation that they do so, I much prefer when said games delve into the culture of their country of origin and Detention definitely does that. The game takes place in 1960s Taiwan during the White Terror, a period when Taiwan was under martial law which began soon after World War II and lasted into the 80s/90s, the longest imposition of martial law in recorded history to that point. The story of the game, unsurprisingly explores some of the difficulties of living in that time and place a great deal (it wouldn't hurt to do a quick Wikipedia skim of the White Terror if you're unfamiliar, but the game makes the important aspects clear enough). Further, many of the puzzles and lore pieces you encounter explore various Taoist and Buddhist concepts and entities, which is unsurprising considering those are the predominant religions of Taiwan. I do appreciate when these games I'm playing don't handhold too much for a Western audience but I will say that without some minimal background in these areas (that I sort of have), you'll likely miss some things, though the main ones necessary for the story are explained explicitly enough.

The gameplay has you controlling Ray in a 2D sidescroller perspective, navigating, mostly, the halls of her school. There's no real platforming like in a lot of 2D games however. Instead gameplay is essentially all reminiscent of an old-school point and click adventure: you click on things to examine, pick them up, or interact with them. Most of the puzzles are resolved by finding the right item to use on a thing. In fact, you can play the whole game one-handed as you really only use the mouse for anything. However, the biggest difference is that as opposed to especially the point and click games of the 90s, Detention is significantly easier. I pretty much never got significantly stuck and even when solutions seem a little less logical, the variables are limited enough you can usually figure it out by poking around anyway. There are a few dangers you have to avoid but not many, and they're easy to avoid if you pay attention to the notes. Despite playing a lot of horror games with puzzles over the years, I still found a lot of uniqueness to the puzzles in this game and while they weren't very hard, most I found clever and enjoyable. The horror is very atmospheric. There are essentially no jumpscares that I recall but the environment is dripping with dread and decay. The atmosphere is very well-done and one of the best parts of the game. It's a much smaller scale but I say it reaches toward the bar set by Silent Hill on atmosphere which, while not quite reaching it, is impressive for a simplistic 2D game.

I could definitely see this game being hit-or-miss for a lot of people. I enjoyed it a lot, but I'm someone who enjoys horror games with puzzles and don't have an issue with dark narratives, even if it's not my usual jam. Though the game can be a little slow-moving with its point and click style, I found it deeply engrossing. However, not everyone will feel this way. If nothing above has put you off, I think Detention would be worth a shot. I would caution that while I play a lot of games, even spooky games, on stream with friends, this is very much a game to play by yourself with focused intention. It's only about 3 hours long and not a huge commitment, but it's impressive the narrative force achieved in a game so short. I also saw that the game has spawned a Netflix series that I plan to give a try. That seems really weird and like it wouldn't work, but I think it's really interesting that a game like this could inspire even a brief TV series so I'm willing to give it a try.